Using PowerTouch
How Do I Adjust the Sound?
2. Touch 
to open the Speaker Level menu:
Although icons for the front speakers appear here, notice that they do not have buttons. They’re here for a visual reference; you cannot change their level.
3.Select a speaker by touching its button. You have selected a speaker when its button darkens.
The two surround speakers (SL and SR) or the two surround back speakers (SBL and SBR) cannot be adjusted independently between each other.
4.Touch the up 
or down arrow 
to adjust the volume of the speaker(s) you chose.
5.Touch 
to return to the previous menu or touch any Quick Access menu button to access that menu.
The subwoofer level can be adjusted between +10 dB and
14